Method for preparing a porous fluoropolymer and preparing an article of same

ABSTRACT

A method of controlling a flow of fluid comprises providing a porous article, the porous article comprising a fluoropolymer and a plurality of pores formed by removing a removable additive, a portion of the pores being connected and establishing fluid flow paths through the article; flowing a fluid through the plurality of pores of the porous article; the fluid comprising a first component having a surface energy less than 40 milliNewton per meter at 25° C. and a second component having a surface energy greater than 40 mN/m at 25° C.; wherein the fluoropolymer is selected such that the first component of the fluid has a better wettability with the fluoropolymer than the second component of the fluid.

CROSS REFERENCE TO RELATED APPLICATION

This application is a divisional application of U.S. Ser. No.13/654,726, filed Oct. 18, 2012, the contents of which are incorporatedby reference herein in their entirety.

BACKGROUND

Separation of homogeneous and heterogeneous fluids has proven to be achallenge. For example, homogeneous fluids, although a single phase, cancontain a combination of different compounds. Of these compounds, onlyone or small number may be of interest, with the other compoundscausing, for example, processing problems. Heterogeneous fluids cancause similar concerns. Implements for the separation of fluidcomponents can be used to arrive at the compounds of interest. Inparticular, downhole completions are often used to produce or harvestfluids, e.g., hydrocarbons, from subterranean reservoirs, formations, orproduction zones. Undesirable fluids, e.g., water or brine, also areoften located downhole. Moreover, such fluids can also containparticulates such as fines. As a result, flow control devices have beencontemplated for limiting production of the undesirable fluids orparticulates in order to maximize the yield of the desirable fluids.Although useful for impeding some amount of water or other undesirablefluid flow or particles, current flow control devices only partiallyeliminate the flow of undesirable fluids or particles. Accordingly,advances in flow control materials, devices, and other systems andmethods for limiting undesirable fluid flow or particles into a downholeproduction assembly are well received by the industry.

BRIEF DESCRIPTION

The above and other deficiencies of the prior art are overcome by, in anembodiment, a method for preparing a porous fluoropolymer precursorcomprises: combining a fluoropolymer and a removable additive to form acomposition, the removable additive having a thermal decompositiontemperature greater than a sintering temperature of the fluoropolymer;compressing the composition to form a preform; and sintering the preformto form the porous fluoropolymer precursor.

In another embodiment, a method for preparing a porous fluoropolymercomprises: disposing the porous fluoropolymer precursor in a removingagent; contacting the removable additive with the removing agent; andremoving, by the removing agent, the removable additive from the porousfluoropolymer precursor to form the porous fluoropolymer, wherein theporous fluoropolymer comprises a plurality of pores formed by removingthe removable additive.

BRIEF DESCRIPTION OF THE DRAWINGS

The following descriptions should not be considered limiting in any way.With reference to the accompanying drawings, like elements are numberedalike:

FIG. 1 shows a picture of a porous polytetrafluoroethylene cylinder;

FIG. 2 shows a 3D image from a computed tomography (CT) scan of theporous polytetrafluoroethylene cylinder of FIG. 1; and

FIG. 3 shows a graph of percentage pressure increase versus flow ratefor samples of oil and water across a cylinder of a porous fluoropolymerformed from a porous fluoropolymer precursor.

DETAILED DESCRIPTION

A detailed description of one or more embodiments is presented herein byway of exemplification and not limitation.

It has been discovered that a porous fluoropolymer exhibits beneficialand selective fluid flow properties. The porous fluoropolymer isthermally and chemically stable and selectively flows fluid therethroughbased in part upon the surface energy of the porous fluoropolymer andthe fluid. Moreover, the porous fluoropolymer impedes passage ofparticulate material that can be entrained in a fluid flow. A methodherein for forming the porous fluoropolymer is rapid and efficient.Furthermore, the method produces a porous fluoropolymer with pore sizefor a given material.

In an embodiment, a method for preparing a porous fluoropolymerprecursor includes combining a fluoropolymer and a removable additive toform a composition. The removable additive has a thermal decompositiontemperature greater than a sintering temperature of the fluoropolymer.The composition is compressed to form a preform, and the preform issintered to form the porous fluoropolymer precursor.

As used herein, “a porous fluoropolymer precursor” means a precursorcomposition or an article made of the precursor composition that isprocessed to produce a porous fluoropolymer. Although the porousfluoropolymer precursor can have voids, pores of the porousfluoropolymer herein are formed by removal of the removable additivefrom the porous fluoropolymer precursor.

The fluoropolymer herein exhibits mechanical, thermal, and chemicalstability and can be a high fluorine content polymer. In an embodiment,the fluoropolymer is completely fluorinated. In another embodiment, thefluoropolymer is partially fluorinated. In some embodiments, thefluoropolymer is a blend of fluorinated polymers, copolymers,terpolymers, or combinations comprising at least one of the foregoingfluoropolymers. The fluoropolymer also can be an oligomer, ahomopolymer, a copolymer, a block copolymer, an alternating blockcopolymer, a random polymer, a random copolymer, a random blockcopolymer, a graft copolymer, a star block copolymer, a dendrimer, orthe like, or a combination comprising at last one of the foregoingfluoropolymers.

In a fluoropolymer that is a copolymer, the repeat units can be acompletely fluorinated, partially fluorinated, or a combinationcomprising at least one of the foregoing. The repeat units of thefluoropolymer can include vinylidene fluoride units, hexafluoropropyleneunits (HFP), tetrafluoroethylene units (TFE), chlorotrifluoroethylene(CTFE) units, perfluoro(alkyl vinyl ether) units (PAVE) (e.g.,perfluoro(methyl vinyl ether) units (PMVE), perfluoro(ethyl vinyl ether)units (PEVE), and perfluoro(propyl vinyl ether) units (PPVE)), or acombination comprising at least one of the foregoing units.

Exemplary fluoropolymers include polytetrafluoroethylene (PTFE,available under the trade name Teflon from DuPont),polyethylenetetrafluoroethylene (ETFE, available under the trade nameTeflon ETFE or Tefzel from DuPont), fluorinated ethylene propylenecopolymer (FEP, available under the trade name Teflon FEP from DuPont),perfluoroalkoxy polymer (PFA, available under the trade name Teflon PFAfrom DuPont), polyvinylidene fluoride (PVDF, available under the tradename Hylar from Solvay Solexis S.p.A.), polyvinylfluoride (PVF,available under the trade name Tedlar from DuPont),polychlorotrifluoroethylene (PCTFE, available under the trade name Kel-Ffrom 3M Corp. or Neoflon from Daikin),polyethylenechlorotrifluoroethylene (ECTFE, available under the tradename Halar ECTFE from Solvay Solexis S.p.A.),chlorotrifluoroethylenevinylidene fluoride (FKM fluorocarbon, availableunder the trade name Viton from FKM-Industries), perfluoroelastomer suchas FFKM (available under the trade name Kalrez from DuPont),tetrafluoroethylene-propylene elastomeric copolymers such as thoseavailable under the trade name Aflas from Asahi Glass Co),perfluoropolyether (available under the trade name Krytox from DuPont),perfluorosulfonic acid (available under the trade name Nafion fromDuPont), and the like. Other exemplary fluoropolymers include copolymersof vinylidene fluoride and hexafluoropropylene and terpolymers ofvinylidene fluoride, hexafluoropropylene, and tetrafluoroethylene.

The fluoropolymer is combined with a removable additive to form thecomposition. The removable additive is an additive that is removedpartially or completely from the fluoropolymer by a removing agent. Whenremoved from the porous fluoropolymer precursor, the removable additiveleaves a pore in the fluoropolymer to form the porous fluoropolymer.Moreover, the removable additive is thermally stable above the sinteringtemperature of the fluoropolymer. According to an embodiment, theremovable additive also has a melting temperature greater than thesintering temperature of the fluoropolymer. Thus, the removable additivedoes not thermally decompose or melt upon sintering of the compositionincluding the fluoropolymer and removable additive when forming theporous fluoropolymer precursor. It is contemplated that materials thatmelt at or below the sintering temperature of the fluoropolymer can bepresent in the porous fluoropolymer precursor. Such materials caninclude an organic acid such sodium benzoate that melts and decomposesat 300° C. In an embodiment, the no such materials that melt at or belowthe sintering temperature of the fluoropolymer are present in the porousfluoropolymer precursor.

According to an embodiment, the removable additive includes an inorganicsalt, glass, or a combination comprising at least one of the foregoingremovable additives.

The inorganic salt can be any salt that can be dissolved by water. Thisincludes salts that are readily soluble with water at 25° C. or thosesparingly soluble at 25° C. Exemplary inorganic salts include a alkalimetal halide (e.g., sodium chloride, potassium chloride, sodium bromide,potassium bromide, and the like), alkaline earth metal halide (e.g.,calcium chloride, magnesium chloride, and the like), ammonium halide(e.g., ammonium chloride, ammonium bromide, and the like), alkali metalnitrates (e.g., sodium nitrate, potassium nitrate, and the like),alkaline earth nitrates (e.g., calcium nitrate, magnesium nitrate, andthe like), alkali metal carbonate (e.g., sodium carbonate, potassiumcarbonate, and the like), alkali metal hydrogencarbonate (e.g., sodiumhydrogen carbonate, potassium hydrogen carbonate, and the like),alkaline earth metal carbonate (e.g., calcium carbonate, magnesiumcarbonate, and the like), ammonium carbonate, ammonium hydrogencarbonate, alkali metal phosphate (e.g., trisodium phosphate,tripotassium phosphate, disodium hydrogen phosphate, dipotassiumhydrogen phosphate, sodium dihydrogen phosphate, potassium dihydrogenphosphate, and the like), diammonium hydrogen phosphate, ammoniumdihydrogen phosphate, and the like. In an embodiment, the inorganic saltis an alkali metal halide such as sodium chloride.

The glass can be a silicon oxide-containing material in a solid,amorphous state without crystallization. Such glass has a high degree ofmicrostructural disorder due to a lack of long-range order. The glasscan include an oxide, for example, silicon dioxide (SiO₂), aluminumoxide (Al₂O₃), barium oxide (BaO), bismuth trioxide (Bi₂O₃), boron oxide(B₂O₃), calcium oxide (CaO), cesium oxide (CsO), lead oxide (PbO),strontium oxide (SrO), rare earth oxides (e.g., lanthanum oxide (La₂O₃),neodymium oxide (Nd₂O₃), samarium oxide (Sm₂O₃), cerium oxide (CeO₂)),and the like.

An exemplary glass is SiO₂ (e.g., quartz, cristobalite, tridymite, andthe like). The glass can include SiO₂ and other components such aselements, for example, aluminum, antimony, arsenic, barium, beryllium,boron, calcium, cerium, cesium, chromium, cobalt, copper, gallium, gold,iron, lanthanum, lead, lithium, magnesium, manganese, molybdenum,neodymium, nickel, niobium, palladium, phosphorus, platinum, potassium,praseodymium, silver, sodium, tantalum, thorium, titanium, vanadium,zinc, zirconium, and the like. The elements can occur in the glass inthe form of oxides, carbonates, nitrates, phosphates, sulfates, orhalides. Furthermore, the element can be a dopant in the glass.Exemplary doped glass includes borosilicate, borophosphosilicate,phosphosilicate, colored glass, milk glass, lead glass, optical glass,and the like.

In an embodiment, the glass can include non-amorphous, crystallinedomains. Such glass can be, for example, a salt or ester of orthosilicicacid or a condensation product thereof, e.g., a silicate. Exemplarysilicates are cyclosilicates, inosilicates, mesosilicates,orthosilicates, phyllosilicates, sorosilicates, tectosilicates, and thelike. These glasses have a structure based on silicon dioxide orisolated or linked [SiO₄]⁴⁻ tetrahedral and include other componentssuch as, for example, aluminum, barium, beryllium, calcium, cerium,iron, lithium, magnesium, manganese, oxygen, potassium, scandium,sodium, titanium, yttrium, zirconium, zinc, hydroxyl groups, halides,and the like.

The removable additive can be present in the composition and porousfluoropolymer precursor in an amount from 1 wt. % to 80 wt. %,specifically 5 wt. % to 80 wt. %, and more specifically 5 wt. % to 75wt. %, based on a weight of the polymer in the composite. The metaldisposed on the carbon material can be present in an amount from 0.5 wt.% to 70 wt. %, 0.5 wt. % to 50 wt. %, and more specifically 0.5 wt. % to30 wt. %, based on the weight of the porous fluoropolymer precursor.

In an embodiment, the removable additive can be any shape and size. Theremovable additive salt can be crystals or grains of various sizes, andthe glass can be pellets, strand, filament, fiber, and the like.Further, the removable additive can be in a powder form.

A size, e.g., a diameter or smallest linear dimension, of the removableadditive is from 50 μm to 500 μm, specifically 75 μm to 500 μm, and morespecifically 100 μm to 450 μm. The removable additive, e.g., of a fiber,can have an aspect ratio from 1 to 1000, specifically 1 to 100, and morespecifically 1 to 10. The removable additive can have a length, orlongest linear dimension, from 100 μm to 1 mm, specifically 100 μm to500 μm, and more specifically 100 μm to 450 μm.

The removable additive has a linear coefficient of thermal expansioneffective such that the removable additive does not expand appreciablyduring sintering the preform. As a result, upon removal of the removableadditive from the porous fluoropolymer precursor (described below), apore in the fluoropolymer formed by removal of the removal additive hasa pore size substantially the same as the size of the removable additivebefore sintering the preform. Thus, the pore size after sintering isfrom 50 μm to 500 μm, specifically 75 μm to 500 μm, and morespecifically 100 μm to 450 μm in the porous fluoropolymer after removalof the removable additive. In an embodiment, the removable additive hasa coefficient of linear thermal expansion such that the pore size in thefluoropolymer is within 10% of the size of the removable additive,specifically 5%, and more specifically 2%.

Combining the fluoropolymer and the removable additive to form thecomposition can include mixing, blending, shaking, stirring and thelike. Here, a fluoropolymer can be a powder such that the removableadditive is added to the fluoropolymer powder. Since the pore size of aporous fluoropolymer formed from this combination of fluoropolymer andthe removable additive is determined, at least in part, by the size ofthe removable additive, combining the fluoropolymer and the removableadditive is contemplated to maintain and not reduce the size of theremovable additive. Although some embodiments employ ball mixing, suchmixing decreases the size of the removable additive through collisions.For aggressive physical mixing that decreases the size of the removableadditive, the removable additive is selected to have an initial sizeeffective to produce a size of the removable additive in the preform(post-mixing the fluoropolymer and the removable additive) from 50 μm to500 μm, specifically 75 μm to 500 μm, and more specifically 100 μm to450 μm. According to an embodiment, the fluoropolymer and the removableadditive are combined in a rotary mixer, acoustic mixer, and the like tomaintain the size of the removable additive during the combining. As aresult, combining the fluoropolymer and the removable additivedistributes the removable additive in the fluoropolymer such that porousfluoropolymer precursor also will have the removable additivedistributed among the fluoropolymer therein. The degree of dispersal ofthe removable additive in the fluoropolymer can be controlled by theamount of mixing such that the final composition of the fluoropolymerand removable additive has a high, low, or moderate degree ofhomogenization. In an embodiment, combining the fluoropolymer and theremovable additive maintains the size of the removable additive towithin 5% of the size of the removable additive before the combining.

After the composition of the fluoropolymer and removable is prepared,the composition can be disposed in a mold. The composition can besubjected to tamping in the mold to settle the composition in the moldso that voids and empty space among the composition and between thecomposition and mold are removed. Subsequent compression of thecomposition in the mold forms the preform. Here, the composition can becompressed under a load from 5,000 to 35,000 pounds, specifically 8,000pounds, to 32,000 pounds, and more specifically 10,000 pounds to 30,000pounds. The load applied to the composition can be selected based on theeffective density of the preform that is desired. Compressing can beperformed at room temperature. In some embodiments, compressing thecomposition occurs at a temperature from 0° C. to 60° C., andspecifically 15° C. to 50° C., which can allow some flow of thefluoropolymer to occur. However, this temperature can be inadequate forsintering the fluoropolymer. The compression of the composition formsthe preform. The preform thus has the shape of the mold in which it wascompressed. As will be appreciated, the mold can be any shape, includingcylindrical, polygonal, round, annular, and the like.

After compressing the composition, the preform is de-molded from themold and subjected to sintering. Sintering the preform forms the porousfluoropolymer precursor. The sintering can be performed by placing thepreform in a heated environment, for example a programmable oven. Thepreform is heated to a temperature effective to fuse together thefluoropolymer. A temperature program including temperature ramp, soak,and cooling ramp can be used for sintering. In an embodiment, a powderof fluoropolymer is used in the composition, which is fused duringsintering. Sintering the preform can be performed without a mold at atemp from 79° C. (175° F.) to 371° C. (700° F.), specifically 87° C.(190° F.) to 371° C. (700° F.), and more specifically 93° C. (200° F.)to 371° C. (700° F.) for a time and at a pressure effective to fuse thefluoropolymer. As discussed with regard to the removable additive, theremovable additive has a melting temperature or thermal decompositiontemperature greater than a sintering temperature of the fluoropolymer.In this manner, the preform converts into a porous fluoropolymerprecursor that includes the fluoropolymer (that has been fused duringsintering) and the removable additive dispersed therein and hassubstantially the same size as in the composition used to form thepreform. The distribution of the removal additive in the porousfluoropolymer precursor can be substantially the same as that in thepreform and composition.

The porous fluoropolymer precursor can be cooled (e.g., to roomtemperature or above) and disposed in a container, e.g., a pressurecooker, bath, sonicator, autoclave, bomb, and the like. In anembodiment, a method for preparing a porous fluoropolymer from theporous fluoropolymer precursor includes disposing the porousfluoropolymer precursor in a removing agent (which also is disposed inthe container); contacting the removable additive with the removingagent; and removing, by the removing agent, the removable additive fromthe porous fluoropolymer precursor to form the porous fluoropolymer.Consequently, the porous fluoropolymer includes a plurality of poresformed by removing the removable additive. Subsequent to forming thepores by removal of the removable additive, the removing agent can flowthrough the plurality of pores, for example, to effect removal ofremovable additive.

Removing the removable additive can be performed at a temperature from60° C. to 90° C., specifically 70° C. to 90° C., and more specifically70° C. to 80° C. and for a time effective for removal of the removableadditive. The time can be selected based on the thickness of the porousfluoropolymer precursor and the extent of removal of the removableadditive desired. In an embodiment, the time for removing is from 1 hourto 8 hours, specifically 2 hours to 6 hours, and more specifically 3hours to 5 hours. The pressure can be any value, including from 1atmosphere to 5 atmospheres. In this manner, the porous fluoropolymer isformed by removing the removable additive from the porous fluoropolymer,leaving pores among the fluoropolymer.

The removing agent is an agent, for example, a compound or compositionthat is effective to remove the removable additive from the porousfluoropolymer precursor. The selection of the removing agent determinesthe ingredients of the removing agent. In an embodiment, the removingagent includes water, which can be effective at elevated temperature forremoving salt from the porous fluoropolymer precursor. In an embodiment,a glass that includes a silicon oxide is removed by, for example,etching by the removing agent such as a fluoride component, which can bepresent with or without an acid. The removing agent also can be, e.g.,an acid or base, e.g., an alkaline solution. A removing agent that isacidic can remove Al₂O₃ from a glass. Moreover, alkaline earth metaloxides (e.g., MgO, CaO, SrO and BaO) in a glass can be removed by analkaline removing agent that also can contain a chelating agent, e.g.,ethylenediaminetetraacetic acid (EDTA).

In an embodiment, the removing agent includes fluorides, bifluorides,tetrafluoroborates, or a combination thereof. Examples of such aremoving agent are, for example, hydrogen fluoride (hydrofluoric acid);ammonium, alkali metal, and antimony fluorides; ammonium, alkali metal,and calcium bifluorides; alkylated ammonium and potassiumtetrafluoroborates; or a combination comprising at least one of theforegoing removing agents. Exemplary removing agents that includefluoride are hydrogen fluoride, ammonium fluoride, fluoroborates,fluoroboric acid, tin bifluoride, antimony fluoride, tetrabutylammoniumtetrafluoroborate, and aluminum hexafluoride. In an embodiment, theremoving agent is water. In some embodiments, the removing agent ishydrogen fluoride, ammonium fluoride, or a combination thereof. Amineral acid such as hydrogen chloride can be added, which can increasethe rate of removal of the removable agent.

The removing agent is effective in removing the removable additive fromthe porous fluorocarbon precursor at a temperature from 15° C. to 100°C., specifically 50° C. to 90° C., and more specifically 70° C. to 90°C. In an embodiment, the removing agent can be activated by input ofenergy, for example, thermal radiation emitted by infrared emitters(e.g., up to about 300° C.), ultraviolet radiation, sonic wavelengths,ultrasonic wavelengths, laser radiation, or a combination thereof.

A solvent can be used with the removing agent. The solvent can bepresent in an amount from 0 wt. % to 90 wt. %, specifically 0 wt. % to50 wt. %, and more specifically 0 wt. % to 20 wt. %, based on the weightof the removing agent. Suitable solvents may be an inorganic solvent,organic solvent, or a combination thereof. Exemplary solvents includewater, alcohols (e.g., methanol, ethanol, and the like), polyhydricalcohols (e.g., diethylene glycol, dipropylene glycol, 1,2-propanediol,1,4-butanediol, 1,3-butanediol, glycerol, 1,5-pentanediol,2-ethyl-1-hexanol, and the like), ketones (e.g., acetophenone,methyl-2-hexanone, and the like), ethers (e.g., ethylene glycolmonobutyl ether, triethylene glycol monomethyl ether, and the like),carboxylic acid esters (e.g., [2,2-butoxy(ethoxy)]ethyl acetate and thelike), esters of carbonic acid (e.g., propylene carbonate and the like),inorganic acids (e.g., hydrofluoric acid, hydrochloric acid, phosphoricacid, sulfuric acid, nitric acid, and the like), organic acids (e.g.,those having an C1-C10 alkyl chain, which is a straight or branchedchain and can be substituted)), or a combination thereof. Examples ofthe solvent include organic carboxylic acids, hydroxy-carboxylic acids,and dicarboxylic acids, such as formic acid, acetic acid, lactic acid,oxalic acid, and the like.

Using the removing agent therefore removes the removable additive fromthe porous fluoropolymer precursor to provide the pores in the porousfluoropolymer. The pores have a size determined by the size of theremovable additive and can be from 50 μm to 500 μm, specifically 75 μmto 500 μm, and more specifically 100 μm to 450 μm. A portion of thepores can be connected and establish a variety of paths through theporous fluoropolymer. Although an embodiment includes some fluid flowpaths via the pores through the porous fluoropolymer, some embodimentshave fluid flow paths through the pores that are tortuous. As a result,the porous fluoropolymer can prohibit, prevent, limit, restrict, impede,or otherwise reduce fluid flow therethrough for providing a pressuredrop thereacross. As used herein, “tortuous” is intended to mean thatthe flow path is circuitous, winding, twisting, meandering,labyrinthine, helical, spiraling, crooked, or otherwise indirect.

The porous fluoropolymer herein has advantageous material properties.The porous fluoropolymer has excellent solvent resistance, electricalinsulating properties, low coefficient of friction, a low flammability,selective permeability based on size or surface energy of an agent fortransmission through the porous fluoropolymer, and high inertness andstability. Moreover, the porous fluoropolymer can be further processedby machining techniques to fabricate the porous fluoropolymer intovarious shaped articles. Machining techniques include drilling, milling,lathing, lapping, cutting, and the like. Further, the porousfluoropolymer has a high melting temperature such that the porousfluoropolymer advantageously can be used over a wide temperature range,for example, from less than 0° C. to 450° C. In an embodiment, theporous fluoropolymer has a thermal decomposition temperature greaterthan 200° C., specifically greater than 300° C., and more specificallygreater than 370° C.

The porous fluoropolymer described herein has many uses. In anembodiment, the porous fluoropolymer is an article. The article can be,for example, a filter, membrane, tubular, sand screen, motor cover,mesh, cover, sheet, or a combination comprising at least one of theforegoing.

Such an article can control the flow of a fluid. As used herein, theterm “fluid” includes a liquid, gas, hydrocarbon, multi-phase fluid,mixture of two of more fluids, water, and a fluid injected from thesurface of the earth downhole (as in hydrocarbon production and thelike) such as water. References to water should be construed also toinclude water-based fluids, e.g., brine or salt water. Subsurfaceformations typically contain water, brine, or other undesirable fluidsalong with oil or other desirable fluids. Herein, within the context ofhydrocarbon production, “water” may be used generally to represent anyundesirable fluid, while “oil” may generally be used to represent anydesirable fluid, although other fluids may be desirable or undesirablein other embodiments.

In one embodiment, the porous fluoropolymer and article thereof are lowsurface energy materials. As used herein, “low surface energy” isintended to mean having a surface energy less than about the lowestsurface energy component of a fluid that contacts the article. Forexample, in an embodiment of an oil/water mixture, the article has asurface energy less than that of oil. Since the surface energy of oil ismuch less than that of water, oil more readily wets a low surface energymaterial, while water molecules form droplets or beads at the surface ofa low surface energy material such as the porous fluoropolymer of thearticle. The fluoropolymers and thus pours fluoropolymer herein, e.g.,made of PTFE, have surface energies less than that of oil, i.e., lessthan approximately 25 or 30 milliNewtons per meter (mN/m). Due to thesurface energy of the article, the article can be configured such that afluid having a surface energy less than 40 milliNewtons per meter (mN/m)at 25° C. has a higher flow rate through the pores of the porousfluoropolymer in the article than a fluid having a surface energygreater than 40 mN/m at 25° C. In another embodiment, the article isconfigured to preferentially flow, through the plurality of pores of theporous fluoropolymer, a low surface energy fluid (e.g., oil, hydrophobiccompound, aliphatic compound), and preferentially impede flow of a fluidhaving a high surface energy (e.g., greater than 40 mN/m), such aswater. In yet another embodiment, the article is configured to impedethe transmission of particles having a diameter greater than the size ofthe pores of the porous fluoropolymer, or less than up to 50% the sizeof the pores due to the tortuous flow paths in the porous fluoropolymer.

The article can be arranged in a variety of ways, e.g., an annularcylinder (a hollow cylinder) comprising the porous fluoropolymer, rod,block, sphere, or any other desired form depending on the shape andconfiguration of the flow path in which the article is installed. Theshape of the article is determined by the mold that is used to make thepreform.

The articles and methods are further illustrated by the followingnon-limiting example.

Preparation Of The Porous Fluoropolymer Precursor. Potassium chlorideand polytetrafluoroethylene powder were weighed on a balancerespectively to provide 92 g each of the fluoropolymer and salt. Thepotassium chloride and polytetrafluoroethylene were transferred to aglass bottle and mixed in a Resodyn acoustic mixer at 70% intensity forone minute on an auto frequency setting. The resultant mixture wasplaced in a mold, which was shook to consolidate the mixture. A total of920 g of PTFE and KCl mixture was added to the mold in five equalportions to make a 4″ long PTFE core. The mixture was compressed in themold using a piston at a limiting force of 15,000 psi with a crossheadtravel speed of 4 inches per minute. The preform, which was a cylinder,was removed from the mold using a hydraulic press and subsequentlysintered in a programmable convention oven. For sintering the preformand making the porous fluoropolymer precursor, the temperature programof the convection oven was as follows: (a) heat to 580° F. with a ramprate of 10° F./minute, (b) hold at 580° F. for 2 hours, (c) heat to 700°F. with a ramp rate of 10° F./min, (d) hold at 700° F. for 3 hours, (e)cool to 550° F. with a ramp rate of 1° F./minute, (g) hold at 550° F.for 2 hours, (h) cool to 180° F. with a ramp rate of 5° F./minute, (i)hold at 180° F. for 3 hours, and (j) cool to room temperature.

Preparation of the Porous Fluoropolymer. The porous fluoropolymerprecursor was weighed, and the size was measured to determine itsinitial weight and dimensions (height and outer diameter). The porousfluoropolymer precursor was disposed in a pressure cooker that washalf-filled with water and heated on a heating plate for 3 to 4 hours.The maximum temperature in the pressure cooker was 100° C. (212° F.).After the heating time, the resulting salt water was drained from thepressure cooker, and the porous polytetrafluoroethylene cylinder waswashed with copious amount of water followed by washing with isopropylalcohol. The porous polytetrafluoroethylene cylinder was then dried in avacuum oven held at 100° C. (212° F.) for 2 hours, cooled, weighed, andmeasured for physical dimensions of height and outer diameter.

The percent porosity was calculated using the following equation: %porosity=(initial weight−final weight)/initial weight*100%. The porouspolytetrafluoroethylene cylinder had a percent porosity of 57%.

FIG. 1 shows a picture of the porous polytetrafluoroethylene cylinder,and FIG. 2 shows a 3D image from a computed tomography (CT) scan of theporous polytetrafluoroethylene cylinder.

Flow Test. The porous tetrafluoroethylene cylinder was flow tested byflowing a sample of oil and water having the following compositions: 0wt. % water (pure oil), 50 wt. % water, and 70 wt. % water, based on thetotal weight of the oil and water sample. The flow rate of each sampleof water and oil was determined using a flow ramp having from 2-6gallons per minute (gpm) with data acquired at 1 gpm increments. Theflow ramps of each sample were repeated three times to verifyrepeatability and reliability of the flow data of the poroustetrafluoroethylene cylinder. The percentage pressure increase (%ΔP) ofeach sample relative to pure oil (i.e., 0% water) across the poroustetrafluoroethylene cylinder is plotted in the FIG. 3.

While one or more embodiments have been shown and described,modifications and substitutions may be made thereto without departingfrom the spirit and scope of the invention. Accordingly, it is to beunderstood that the present invention has been described by way ofillustrations and not limitation. Embodiments herein are can be usedindependently or can be combined.

All ranges disclosed herein are inclusive of the endpoints, and theendpoints are independently combinable with each other. The suffix “(s)”as used herein is intended to include both the singular and the pluralof the term that it modifies, thereby including at least one of thatterm (e.g., the colorant(s) includes at least one colorants). “Optional”or “optionally” means that the subsequently described event orcircumstance can or cannot occur, and that the description includesinstances where the event occurs and instances where it does not. Asused herein, “combination” is inclusive of blends, mixtures, alloys,reaction products, and the like. All references are incorporated hereinby reference.

The use of the terms “a” and “an” and “the” and similar referents in thecontext of describing the invention (especially in the context of thefollowing claims) are to be construed to cover both the singular and theplural, unless otherwise indicated herein or clearly contradicted bycontext. “Or” means “and/or.” It should further be noted that the terms“first,” “second,” and the like herein do not denote any order,quantity, or importance, but rather are used to distinguish one elementfrom another. The modifier “about” used in connection with a quantity isinclusive of the stated value and has the meaning dictated by thecontext (e.g., it includes the degree of error associated withmeasurement of the particular quantity). The conjunction “or” is used tolink objects of a list or alternatives and is not disjunctive; ratherthe elements can be used separately or can be combined together underappropriate circumstances.

What is claimed is:
 1. A method of controlling a flow of fluid, themethod comprising: providing a porous article, the porous articlecomprising a fluoropolymer and a plurality of pores formed by removing aremovable additive, a portion of the pores being connected andestablishing fluid flow paths through the article; flowing a fluidthrough the plurality of pores of the porous article; the fluidcomprising a first component having a surface energy less than 40milliNewton per meter at 25° C. and a second component having a surfaceenergy greater than 40 mN/m at 25° C.; wherein the fluoropolymer isselected such that the first component of the fluid has a betterwettability with the fluoropolymer than the second component of thefluid.
 2. The method of claim 1, wherein the fluoropolymer impedes theflow of the second component of the fluid more than the first componentof the fluid.
 3. The method of claim 1, wherein flowing the fluidthrough the pores of the porous article is conducted in a downholeenvironment.
 4. The method of claim 1, wherein the fluoropolymer ispartially fluorinated.
 5. The method of claim 1, wherein thefluoropolymer is completely fluorinated.
 6. The method of claim 1,wherein the fluoropolymer comprises polytetrafluoroethylene,polyethylenetetrafluoroethylene, fluorinated ethylene propylenecopolymer, perfluoroalkoxy polymer, polyvinylidene fluoride,polyvinylfluoride, polychlorotrifluoroethylene,polyethylenechlorotrifluoroethylene, chlorotrifluoroethylenevinylidenefluoride, perfluoroelastomer, tetrafluoroethylene-propylene elastomericcopolymer, perfluoropolyether, perfluorosulfonic acid, or a combinationcomprising at least one of the foregoing fluoropolymers.
 7. The methodof claim 1, wherein a size of the plurality of pores is from 50 μm to500 μm.
 8. The method of claim 1, wherein the article comprises a flowcontrol device, filter, membrane, tubular, sand screen, motor cover,mesh, cover, sheet, or a combination comprising at least one of theforegoing.
 9. The method of claim 1, further comprising forming theporous article.
 10. The method of claim 8, wherein forming the porousarticle comprises: combining the fluoropolymer and a removable additiveto form a composition , the removable additive having a thermaldecomposition temperature greater than a sintering temperature of thefluoropolymer; compressing the powder composition to form a compressedcomposition; sintering the compressed composition to form a preform;disposing the preform in a removing agent; contacting the removableadditive with the removing agent; and removing, by the removing agent,the removable additive, from the preform to form the porous article. 11.The method of claim 10, further comprising: disposing the powdercomposition in a mold prior to compressing the powder composition; andremoving the compressed composition from the mold before sintering thecompressed composition.
 12. The method of claim 10, wherein combiningthe fluoropolymer and the removable additive distributes the removableadditive in the fluoropolymer, and the compressed composition has theremovable additive distributed among the fluoropolymer.
 13. The methodof claim 10, wherein sintering the compressed composition is performedat a temperature from 79° C. (175° F.) to 371° C. (700° F.).
 14. Themethod of claim 10, wherein the removable additive is the glass pellets,strand, filament, or fiber which comprises silicon dioxide, aluminumoxide, barium oxide, bismuth trioxide, boron oxide, calcium oxide,cesium oxide, lead oxide, strontium oxide, a rare earth oxide, lanthanumoxide, neodymium oxide, samarium oxide, cerium oxide, or a combinationcomprising at least one of the foregoing glasses.
 15. The method ofclaim 14, wherein the glass pellets, strand, filament, or fibercomprises a dissolvable glass.
 16. The method of claim 10, wherein theremovable additive is present in the porous fluoropolymer precursor inan amount from 1 wt. % to 80 wt. %, based on the weight of the porousfluoropolymer precursor.
 17. The method of claim 10, wherein a size ofthe removable additive is from 50 μm to 500 μm.
 18. The method of claim10, wherein the melting temperature of the removable additive is greaterthan the sintering temperature.
 19. The method of claim 10, furthercomprising flowing the removing agent through the plurality of pores.20. The method of claim 10, wherein removing the removable additive isperformed at a temperature from 60° C. to 90° C.
 21. The method of claim10, wherein the removing agent comprises water, hydrogen fluoride,ammonium fluoride, alkali metal fluoride, antimony fluoride, ammoniumbifluoride, alkali metal bifluoride, calcium bifluoride, alkylatedammonium tetrafluoroborate, potassium tetrafluoroborate, fluoroboricacid, tin bifluoride, tetrabutylammonium tetrafluoroborate, aluminumhexafluoride, or a combination comprising at least one of the foregoingremoving agents.